(105e) Physicochemical Properties of Diesel Exhaust Particles Collected during Inhalation Exposure Studies

Diesel exhaust and especially diesel exhaust particles (DEP) are a health concern because of their complex chemistry, small size, and ubiquitous presence in urban environments. As part of a research program designed to relate diesel exhaust properties to adverse health effects, a series of inhalation exposure studies were conducted to investigate the propensity of diesel exhaust to promote cardiopulmonary diseases, immune polarization, and trans-generational effects in mice. Three diesel engines were utilized to generate diesel exhaust for whole animal exposures. These include a four cylinder 31 kW non-catalyst equipped engine and air compressor (CDEP), an eight cylinder 134 kW mid-1990s vintage pickup truck engine equipped with an oxidation catalyst and eddy current dynamometer (TDEP), and a one cylinder 4.8 kW non-catalyst equipped engine and generator (GDEP). The CDEP and TDEP engines were operated at approximately 25% of their maximum engine loads at speeds of 1700 and 2500 rpm, respectively. These operating conditions were chosen to be representative of typical equipment operation, and for TDEP, to imitate steady-state highway driving. The GDEP engine was operated at approximately 80% of its maximum load at 3600 rpm. This also was intended to be representative of how a small generator might be used. During the exposures, gas/particle concentrations and particle size distributions were monitored in real-time. DEP was collected at engine exhaust and inhalation chamber locations using filters, baghouses, and/or an electrostatic precipitator, and analyzed for particle mass concentration, organic and elemental carbon (OC-EC), inorganic (non-EC) elements, and organic components. Dichloromethane-extracted organic material (EOM) was sequentially sub-fractionated through a silica column using four organic solvents of increasing polarity: hexane, 50:50 hexane:dichloromethane, dichloromethane, and methanol. The EOMs and the sub-fractions were also determined gravimetrically. The exhaust particle mass concentration of the CDEP was approximately 11 times greater than either the TDEP or GDEP. This also corresponded to higher amounts of quantifiable polycyclic aromatic hydrocarbons (PAHs) in the CDEP samples (>400 μg/g) compared to the TDEP and GDEP samples (<100 μg/g). Geometric mean number diameters of the CDEP was slightly larger (84-102 nm) than the TDEP and GDEP (48-74 nm). However, with the exception of PAH species, other organic chemical components were similar for all three engines. Sulfur, chlorine, zinc, calcium, and iron were the most abundant inorganic elements, comprising <5% of the mass. OC/EC mass ratios ranged from 0.2-2.0. EOM comprised 10-40% of the DEP mass, and partitioned at 54-77% and 8-13% between the least-polar (hexane) and most-polar (methanol) solvents, respectively. Less than 2.5% of mass of all DEP samples was identified and quantified as specific organic compounds, and 84-98% of the organics identified were alkanes or organic acids. The overall characteristics placed the three EPA-generated DEP samples between the NIST SRM2975 and Japanese (Sagai) samples, which are commonly used as reference samples but have drastically different properties from each other (This abstract does not reflect EPA policy.).